Continuous process for determining moisture content and heat of combustion of solid fuels



Dec. 14, 1965 CONTINUOUS PROCESS FOR DETERMINING MOISTURE CONTENT AND HEAT OF COMBUSTION OF SOLID FUELS Filed March 8, 1962 MESSER 2 Sheets-Sheet l sou c5 20\ H T CONT Com 0 60350 F/g.

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CONTINUOUS PROCESS FOR DETERMINING MOISTURE CONTENT AND HEAT OF COMBUSTION 0F SOLID FUELS Filed Mar'h s, 1962 2 Sheets-Sheet 2 1M2 K I 4; AT VALUE 0; 00A; JAMPlL-S 4 000 am ecu yaw 15M United States Patent 3,222,927 CONTINUOUS PROCESS FOR DETERMINING MOISTURE CONTENT AND HEAT OF COM- BUSTION OF SOLID FUELS Leonard Messer, P.O. Box 231, Pittsburgh, Pa. Filed Mar. 8, 1962, Ser. No. 178,377 13 Claims. (Cl. 73-190) This invention relates to a process for obtaining a more representative indication of the heat value characteristics of solid type fuels or the like, such as coal.

Producers and users of solid fuel, such as coal have heretofore obtained heat value data in connection with the fuel received, used or reduced to a product for sale, by means of methods which have required expensive equipment and skilled individuals trained in the work. The data so received, while precise, may not be representative because of the discontinuous sampling of the product stream of the solid fuel while the destructive nature of the method rendered any continuous sampling impracticable. The process of the present invention is therefore designed to render a continuous indication of the heat value of solid type fuel being continuously conveyed in a product stream as for example in coal washeries, coke and briquette plants or on coal conveying apparatus of large scale power users.

Another object of this invention is to provide a continuous and non-destructive process for solid type fuel, such as coal being continuously conveyed in a product stream for obtaining indication of the heat value of this fuel. Although the instantaneous heat value measurements obtained by the present process are not precise, the process is sufficiently accurate in connection with coal having a limited range of ash content variation and in connection wtih coal originating from a common origin or seam so that relatively constant analysis factors are available for properly calibrating the apparatus of the process, to obtain more reliable and representative data. As a result, useful heat value information may be obtained in a continuous, automatic and inexpensive manner which may be desired by large scale power users anxious to check the quality of the fuel being received as well as by coal washery and coke plant operators desirous of furnishing customers with fuel grade information.

The process of the present invention is somewhat related to the proximate analysis of coal wherein physical means are utilized to separate coal into four parts by percentages, namely moisture, volatile matter, fixed carbon and ash. However, unlike the proximate analysis methods the present invention does not involve the destructive tests associated with proximate analysis methods nor the same degree of measurement precision and further is restricted to obtaining data in connection with moisture and ash content only. The moisture and ash content constituting the nonburnable portions of the fuel, may therefore provide sufiicient data for obtaining a sufficiently accurate heat of combustion indication of the solid fuel being tested. It has been found that within any operative range to which the present process is related, the heat energy available from coal in terms of B.t.u. for a given moisture content, will aproximate a linear function of the ash content. Accordingly, with the proper calibration and information as to the ash content range and with moisture content calculating facilities, a useful heat value indication may be provided in a continuous manner in terms of B.t.u. per unit weight, calories per gram, etc.

In accordance with the foregoing objects, the solid particles of fuel or coal may be sampled from a product stream either continuously, or intermittently so as to establish a sample stream of the solid fuel. Continuous 3,222,927 Patented Dec. 14, 1965 ash content measuring devices or systems have been developed for providing continuous ash content information from such sample streams. However, the sample stream of coal must be properly conditioned for measurement by the ash content measuring device. The conditioning of the sample stream of coal involves therefore the reduction of the coal to a suitable particle size range, uniform distribution of the particles in a layer and reduction of the inherent moisture of the solid fuel to a uniform low value. In conditioning the solid fuel in the sample stream for ash content measuring purposes, it has also been found useful to determine the reduction in unit weight of the fuel in the sample stream by virtue of the release of moisture therefrom. This information while not being a true indication of the moisture content itself, is an index thereof and does provide an indication of relative variations in the moisture content of the fuel be ing sampled so that when properly calibrated with the ash content information furnished by the ash content measuring device, the data may be fed to a data calculating device, the output of which will provide instantaneous heat of combustion readings. The sample stream of solid fuel may thereby furnish the desired information after which it may be supplied to other processing steps or returned to the product stream as desired.

These together with other objects and advantages which will become subsequently apparent reside in the details of construction and operation as more fully hereinafter described and claimed, reference being had to the accompanying drawings forming a part hereof, wherein like numerals refer to like parts throughout, and in which:

FIGURE 1 is a flow diagram illustrating the process of the present invention.

FIGURE 2 is a flow diagram illustrating a modification of the process as illustrated in FIGURE 1.

FIGURE 3 is a diagrammatic illustration of typical apparatus that may be utilized in connection with the process as illustrated in FIGURE 1.

FIGURE 4 is a graphical illustration of typical heat value data obtained from a sample of fuel for calibrating the apparatus of the process.

Referring now to the drawings in detail, attention is initially invited to FIGURE 1 wherein the basic process of the present invention is illustrated. A solid fuel in the form of coal may therefore be conveyed by any suitable conveyor mechanism 10 along a product stream 12 from which a portion of the solid fuel is diverted into a sample stream 14 either continuously or intermittently by suitable sampler mechanism 16. The sample stream of solid fuel is then fed into a conditioning unit 18 to which heat is supplied from any suitable source 20 for the purpose of reducing the fuel to a uniform inherent moisture content Depending upon the physical condition of the solid fuel dimensionwise, the conditioning unit may also reduce the solid fuel to a predetermined particle size range and also mix the fuel particles so that it may be conveyed in the sample stream as a uniformly distributed layer. Accordingly, the sample stream will be conditioned so that ash content information may be accurately obtained therefrom by the ash content measuring device 22 which is of the continuously operating type. A differential weighing device 24 is also provided for the purpose of obtaining information as to the change in unit weight of the sample stream passing through the conditioning unit by virtue of the release of moisture therefrom. The information output 26 from the differential weighing device and the output 28 from the ash content measuring device are fed to a data calculating device 30 as variable inputs thereto so that the output thereof may be fed to a meter or recorder 34 to furnish the calorific information in the form of B.t.u. per unit weight of the production stream 12. The meter or recorder 34 will therefore provide a continuous indication of the fluctuating heat value of the solid fuel in'theproduct'stre'am 12. It will also be ob served, that the sample stream diverted from the production stream 12, may be supplied to other apparatus for treatment thereof if desired to obtain additional data or the sample stream may be returned to the product stream as desired.

Referring now to FIGURE 2, it will be observed that the process illustrated therein is the same as that illustrated in FIGURE 1 except for the manner in which the moisture content indication or information is obtained. The process illustrated in FIGURE 2 therefore, does not involve any differential weighing device but instead measures the flow rate of the moisture released from the conditioning unit 18 by any suitable continuously operative fluid flow measuring device 36 the output 38 of which may be calibrated to provide an index of the moisture content per unit weight of the sample stream 14. The output 38 of the fluid flowing measuring device is therefore fed to the calculator 30 with the output 38 of the ash content measuring device 22. The process of FIGURE 2 is otherwise the same as that of FIGURE 1.

It will therefore be apparent that in both cases, the variation in either the weight measurement or flow rate reading will reflect the variation in moisture content of the product stream 12 as it moves past the sampler 16.

Referring now to FIGURE 3 in particular, one typical process installation is diagrammatically illustrated. It will be observed therefore, that a product stream 12 of solid coal is deposited upon the continuously moving conveyor 10. The continuous conveyor mechanism may for example be part of the equipment of a large scale power installation supplying the stream 12 of fuel to the power generating equipment. A sampling mechanism 16 is therefore provided in order to divert a portion of the product stream onto a Weighing conveyor device 40 from which the sample stream 14 is deposited within the conditioning unit 18. The sample stream of fuel will be air dried within the conditioning unit 18 preferably with air at 110 C. so as to reduce the moisture content thereof to approximately one percent. The conditioning unit 18 may further be operative to crush the fuel particles and screen it so as to reduce it to a particle size which is uniform and further mix the particles Within a drum for uniform weight distribution of the particles when conveyed along the conveyor device 42. The sample stream of conditioned coal 44 may therefore be suitable for obtaining ash content information therefrom by an X-ray type of continuous .ash content measuring device 22. The conditioned sample stream 44 is therefore delivered to the conveyor 42 from a second weighing conveyor 46 operative simultaneously with the first weighing conveyor device 40 on the differential weighing device 24 to provide information as to the moisture content of the diverted sample stream 14. The scale 48 of the differential weighing device 24 may therefore be calibrated for such purpose. Information will therefore be continuously available as to the moisture content of the product stream 12. The output indicator 50 is however operatively connected by a suitable output linkage 26 to the calculating device 30 for purposes as described with respect to FIG- URE 1.

The practicality of the continuous heat value indicating process of the present invention has been made possible by the development of a continuous ash content indicating device 22 of theX-ray type. This type of device involves the passing of the sample stream 44 beneath a split beam from an X-ray tube and measuring the intensity of the diffuse reflections (1,) after the sample stream has been conditioned by reduction of its moisture content to a constant moisture level. The intensity of the difliuse reflections will be reduced from the intensity of the incident X ray radiation (I by an amount dependent upon the radiation absorption of the moving layer of coal 44.

. they differ from each other considerably.

Absorption data for coal is specified by an absorption coefficient u where a a+ b b u being the absorption coefficient of the ash portion of the coal and u the absorption coefficient of the combustible portions of the coal while g and g, are respectively the relative quantities by weight of the ash and combustible portions of the coal. Inasmuch as the value of the absorption coeflicient of the ash and combustible portions of the coal will vary slightly for coal from a common origin, these values may be considered constant although Accordingly, the value of the coal absorption coefficient u from the foregoing formula, will depend upon the relative quan-' a constant even though the moisture content of the product stream 12 varies. Thus, by measuring the diffuse reflection intensity, the coal absorption coefiicientu may be obtained which is an index of the ash content since it can be shown that where A and B are constants. The scale 54 of the ash content measuring device 22 may thereby be calibrated to provide continuous information as to the percentage ash content of the coal moving along the product stream 12. The scale indicator for the scale 54 is therefore connected by suitable output linkage 28 to the calculator 30 for controlling one variable input thereto while another input thereof is controlled by the output linkage 26 from the differential weighing device 24. The output 32 from the calculator 30 will therefore be some linear function of the percentage ash content as measured by device 22, this factor being varied by variations in moisture content as measured by device 24 so as to take this variable factor into account when obtaining the heat value of the fuel. As indicated in FIGURE 4, for a given moisture content, the heat value of a typical coal sample has been found to vary between 6000 and 15,400 B.t.u. per unit weight as a linear function of percent of ash per unit weight of coal. Accordingly, with information such as depicted in FIGURE 4, the recorder 34 may be adjusted or calibrated so as to provide the heat value information as a substantially linear function of the output of the ash measuring device representing the calorific value of the coal being sampled c'orrected however through the calculator 30 for any variation in moisture content. The recorder 34 is therefore suitably geared to the conveyor mechanism 10 so as to provide continuous indication of the actual heat value of the product stream 12 in proper proportion to movement of the stream so that the calorific value readprocess of the present invention will be apparent. It will also be appreciated, that the process may be utilized in connection with data obtained from the treatment of the sample stream by further analysis steps that may be applied. to the conditioned sample stream 44." The information retained on the recorder 34 will therefore be available without the useof trained personnel capable of only rendering incomplete, periodic sampling tests of the product stream 12. Also, the recorded information from the recorder 34 may be furnished with its associated batch of coal by the supplier to the consumer as an attractive service Without involving any great expense to the supplier. Alternatively, the process of the present invention may be utilized by the consumer such as a large: scale power producer to provide an inexpensive and con tinuous check on the grade or quality of the fuel being received. It should also be appreciated, that while the process has been described in conjunction with an X-r-ay type ash analyzer, any other ash analyzer from which a suitable output is available, may be utilized.

The foregoing is considered as illustrative only of the principles of the invention. Further, since numerous modifications and changes will readily occur to those skilled in the art, it is not desired to limit the invention to the exact construction and operation shown and described, and accordingly all suitable modifications and equivalents may be resorted to, falling within the scope of the invention as claimed.

What is claimed as new is as follows:

1. A non-destructive method for providing instantaneous calorific information in connection with a solid particle fuel exhibiting a heat value characteristic which is a substantially linear function of ash content only for a constant value of moisture content comprising the steps of: diverting a sample flow of solid fuel particles from a continuous product flow thereof; reducing the moisture content of the sample flow of solid particles to a predetermined constant level; simultaneously determining the instantaneous rates of product flow movement and quantitive moisture content reduction measuring the instantaneous ash content of the sample flow at said constant moisture level calibrated in accordance with said linear function; recording a said calibrated ash content measurements at a rate porportional to said determined rate of product flow movement to identify the portion of the product from which the sample flow is derived; and calculating the instantaneous calorific value of said fuel from the ash content measurement, the moisture content reduction and the product flow rate.

2. The combination of claim 1, wherein instantaneous calibrated indications are simultaneously provided respectively reflecting variations in moisture content and ash content of the product flow of fuel.

3. The combination of claim 2, wherein said sample flow is weighed prior to and subsequent to reduction in moisture content for a differential indication of said quantitative rate of moisture content reduction.

4. The combination of claim 1, wherein said sample flow is weighed prior to and subsequent to reduction in moisture content for a difierential indication of said quantitative rate of moisture con-tent reduction.

5. The combination of claim 1, wherein the flow rate of moisture released as a result of said reduction in moisture content is measured to provide said quantitative rate of moisture content reduction.

6. The combination of claim 5, wherein continuous calibrated indications are simultaneously provided respectively reflecting variations in moisture content and ash content.

7. In combination with a method of nondestructively determining the ash content of sampled coal after being dried to a constant low moisture level, the steps of: sampling the coal from a product flow having an unknown variable moisture content; measuring the release of moisture from each sample of coal after being dried to said constant moisture level; calculating a heat value of each sample from the ash content determinations of the constant moisture level sample and from variations in the measured release of moisture from the sampled flow; determining the rate of movement of the product flow being sampled; and correlating said heat value of each sample with said determined rate of movement for providing a heat value indication for each sample of coal identified with the portion of the product flow from which it was sampled.

8. A coal sampling process in which heat value readings are to varied in dependence on fluctuation in the ash content of the coal to be sampled and the moisture content thereof comprising the steps of: preparing each sampling of coal for measurement of dispersion capacity by reducing the unknown moisture content thereof to a constant predetermined moisture level; regularly measuring radiation dispersion capacity of coal samples from a product stream having an unknown variable moisture content regularly measuring the fluctuating reductions in moisture content of each sample of coal prior to measuring of the respective dispersion capacities; performing calculations with the dispersion capacity measurements and said fluctuations in the reduction of moisture content to provide said heat value readings and continuously identifying the heat value reading of each sample with the portion of the product stream from which it was sampled.

9. A method for providing calorific information in connection with a product flow of fuel having a variable unknown moisture content without measurement of energy released therefrom comprising the steps of: sampling fuel from said product flow; drying each sample of fuel to a constant moisture level; measuring the fluctuating reductions in moisture content of the sample produced by said drying; measuring the ash content of each sample after drying; calculating the heat value 'of each fuel sample from the ash content measurements of thereof and the fluctuation of the previously measured moisture content reduction of the same sample; and identifying the calculated heat value of each sample with a portion of the product flow from which the sample was sampled.

10. A method of providing calorific information for a moving stream of combustible matter exhibiting a heat value characteristic which is a substantially linear function of ash content for a constant percentage of moisture content comprising the steps of: regularly sampling said moving stream of combustible matter having an unknown moisture content; drying each sample of combustible matter for reducing the moisture content thereof to a predetermined constant moisture level; measuring the amount of moisture removed from each sample during drying; measuring the ash content of each sample at said predetermined moisture level; calculating the heat values from said ash content measurements and fluctuations in said amounts of moisture removed during drying of the samples; and continuously identifying the calculated heat values of the samples with portions of the moving stream of combustible matter from which the respective samples were obtained.

11. The method of claim 10 wherein said calculated heat values are determined in accordance with said linear function of ash content for a constant moisture content, said ash content measurements being obtained by subjecting each sample to radiation and measuring the intensity of diffuse reflections of said radiation.

12. The method of claim 11, wherein the calculated heat values are continuously identified by: instantaneously determining the rate of movement of the moving stream; imparting movement to a record proportional to said rate of movement; and recording said heat values of the samples on the record when being moved \at rates proportional to movement of the moving stream at the instant the respective samples are obtained therefrom.

13. The method of claim 10 wherein the calculated heat values are continuously identified by: instantaneously determining the rate of movement of the moving stream; imparting movement to a record proportional to said rate of movement; and recording said heat values of the samples on the record when being moved at rates proportional to movement of the moving stream at the instant the respective samples are obtained therefrom.

References Cited by the Examiner UNITED STATES PATENTS 1,08 8,280 2/1914 Hottinger 73-193 2,860,252 11/1958 Dijkstra 25051.5

FOREIGN PATENTS 802,521 10/ 1958 Great Britain.

RICHARD C. QUEISSER, Primary Examiner. JOHN P. BEAUCHAMP, Examiner. 

1. A NON-DESTRUCTIVE METHOD FOR PROVIDING INSTANTANEOUS CALORIFIC INFORMATION IN CONNECTION WITH A SOLID PARTICLE FUEL EXHIBITING A HEAT VALUE CHARACTERISTIC WHICH IS A SUBSTANTIALLY LINEAR FUNCTION OF ASH CONTENT ONLY FOR A CONSTANT VALUE OF MOISTURE CONTENT COMPRISING THE STEPS OF: DIVERTING A SAMPLE FLOW OF SOLID FUEL PARTICLES FROM A CONTINUOUS PRODUCT FLOW THEREOF; REDUCING THE MOISTURE CONTENT OF THE SAMPLE FLOW OF SOLID PARTICLES TO A PREDETERMINED CONSTANT LEVEL; SIMULTANEOUSLY DETERMINING THE INSTANTANEOUS RATES OF PRODUCT FLOW MOVEMENT AND QUANTITIVE MOISTURE CONTENT REDUCTION MEASURING THE INSTANTANEOUS ASH CONTENT OF THE SAMPLE FLOW AT SAID CONSTANT MOISTURE LEVEL CALIBRATED IN ACCORDANCE WITH 